The Sustainable Future of Wooden Skyscrapers

Michael Green says his wooden towers can help offset climate change. Can he find a client willing to go out on a limb and build one?

Michael Green believes that his son, Makalu, might be the youngest person in history to visit all seven continents. It’s plausible. Makalu was 10 years old in January 2012, when he and his father saw their seventh, Antarctica. Over three weeks, they sailed on a 50-passenger ship down the Antarctic Peninsula, a region where temperatures have risen more in the last five decades than anywhere else on Earth. Toward the end of their trip, father and son passed the embayment left by the collapse of the Larson B, an ice shelf the size of Rhode Island that slid into the ocean in 2002. “When [Makalu’s] 40, I hope he takes his son to Antarctica to see how much the landscape has changed,” Green says. It was a firsthand reminder about why he is striving to transform the architecture of our cities with a radical idea: wooden skyscrapers.

“Architecture hasn’t seen a new structural system—a new approach to big building—in a hundred years,” says Green, 46, the founding principal of Vancouver-based Michael Green Architecture (MGA) and a fellow of the Royal Architectural Institute of Canada. “The face of architecture has always been contingent on a structural system. Modernism came about because of steel and concrete and our ability to move large scales of stuff around.”

The load-bearing steel skeleton helped give rise to the modern skyscraper in the late 1880s, and just after the turn of the century, developments in reinforced concrete—cheap, strong, durable, soundproof, nearly fireproof, and possessing a high thermal inertia—made it nearly the perfect building material for high-density urban structures.

The problem: The production of both concrete and steel emits tremendous levels of carbon dioxide, the primary greenhouse gas responsible for anthropogenic climate change. Most problematic is the manufacture of cement, the binding agent in concrete, in which kilns of limestone are heated upwards of 2,600 F, typically with coal—a process responsible for 5 percent of the world’s annual carbon emissions. The production of steel, even more energy-intensive, accounts for 3 percent.

Those carbon emissions will likely increase as architects confront another crisis: the world’s shortage of affordable housing. According to U.N.-Habitat, 1 billion people live in slums, a figure that the agency says is on pace to reach 3 billion by 2050.

To tackle this issue, the U.N. announced, in its Millennium Declaration, its intent to house 100 million slum residents by 2020. Meanwhile, in China, where over a third of city-dwellers live in slums, the government has embarked on a plan to build 36 million affordable-housing units by 2015—projects that will likely be built using concrete.

“There hasn’t been any reason to innovate until now,” says Green, who argues that the need for so much new housing will contribute to climate change if there isn’t a systemic structural shift in high-density urban construction. “Green carpet, green roofs, solar panels—they’re relatively minor fixes,” he says. Building with wood, he says, would not only limit the creation of carbon dioxide associated with the production of concrete and steel, but it also has another benefit: carbon storage. Trees sequester carbon through photosynthesis; when they decompose, that carbon is re-released into the atmosphere. But when you build using wood, the carbon remains stored for the life of the building. A typical North American timber-frame house stores 28 tons of carbon dioxide, roughly the amount emitted by a mid-size car over seven years.

As Green often says, “Man can’t compete with photosynthesis.” But here’s the real question: If you’re a developer building a skyscraper, can wood compete with concrete and steel?

Five years ago, as an arts-and-crafts project, Green and his son made an 18-inch wooden skyscraper out of sticks and foam board. As Green recalls, when he showed it to Eric Karsh, a structural engineer he often partners with, Karsh said, “Yeah, this works. Let’s talk about it.” With a grant from the Canadian Wood Council, which represents the country’s wood manufacturers, they began researching how to make that model a reality.

Last March, they compiled their findings in a weighty white paper, “The Case for Tall Wood Buildings.” Peer-reviewed by two structural engineering firms, it shows how high-rises might be built out of giant panels of engineered wood, known as mass timber. It comes in several forms, all made from the scraps of fast-growth trees, including aspen and birch, that are bonded with formaldehyde (at levels well below what the U.S. Department of Housing and Urban Development considers potentially carcinogenic). Green intends to build primarily with cross-laminated timber, invented in Europe in the 1990s.

The report offers structural diagrams for four building prototypes: 12 stories, with a wooden structural core, no structural walls, and a flexible floor plan suitable for commercial or residential use; 20 stories with either interior or exterior structural walls, both better-suited to residential use; and 30 stories, with interior and exterior structural walls, and a rigid layout solely suited for residential use. In each prototype, the floor slabs, elevator and stair cores, and structural walls are made of mass timber. Linking those panels are wide-flange steel beams, designed to lend ductility to the structures in the event of an earthquake. The foundations are reinforced concrete. To erect these buildings, Green proposes a balloon-frame method, in which six stories are tilted up at a time.

The biggest concern? Fire. But the sheer size of mass-timber panels makes them far less combustible than 2x4s, just as logs are harder to ignite than kindling. Additionally, when a mass-timber panel is exposed to flames, its exterior chars, insulating the inner wood and containing the fire for more than an hour. The material has also performed as well as concrete and steel in seismic and acoustic tests. But the biggest advantage, Green says, is how quickly and quietly mass timber high-rises can be built compared to their concrete and steel counterparts—and, according to Green’s estimates, for the same price.

A notable caveat: Wooden buildings only offset carbon emissions if their wood comes from sustainably harvested forests, such as those in Canada, where the annual rate of deforestation is less than 1 percent. But if Green attempts to bring wooden skyscrapers to China, where the timber industry is far less regulated, deforestation will be a larger obstacle.

For now, Green doesn’t envision mass timber replacing concrete and steel as the sole dominant urban building material; he simply wants to provide a more sustainable alternative—and an incentive for the steel and concrete industries to reduce their carbon emissions. “We’re trying to make wood competitive,” he says. But his long-term ambitions are anything but modest: “We want to go from log cabins to Shangri La.”

Green was drawn to architecture at an early age. His maternal grandfather, Richard Bennett, worked as a draftsman for Edward Durrell Stone and served as the chairman of the Yale Department of Architecture in the 1940s. When Green was a teenager, his paternal grandfather helped him build a wooden cottage on Michigan’s Upper Peninsula.

He received his bachelor’s degree from Cornell’s School of Architecture in 1989. “It’s a bloody hard school, and I had a hard time,” he says. Of the half-dozen longtime professors I contacted, only one remembered him—primarily because of their shared love of ice-climbing.

After Cornell, Green went to work for César Pelli and contributed to the renovation of Ronald Reagan National Airport. In 2002, after a stint with Vancouver-based Architectura, he and his colleague Steve McFarlane left to create their own firm, which later became McFarlane Green Biggar Architecture + Design (MGB). But Green’s ambitions to build tall eventually clashed with his partners’ commitment to more traditional residential projects, and after nine years at the firm he founded his own practice in March 2012, joined by 15 former MGB employees.

One of the main hindrances to Green’s quest has been building codes, which in North America have long restricted heights of wooden buildings because of the potential fire risks. In 2009, the British Columbia Building Code raised the maximum height from four to six stories, but the research informing the code remains based on stick-frame construction. Building codes for wood construction in Europe are less strict—in London, Waugh Thistleton Architects designed a nine-story mass-timber apartment building that went up in 2011, and in Kirkenes, Norway, Reiulf Ramstad Architects is designing a 16-story timber tower.

Although Green eventually wants to build wooden skyscrapers as affordable-housing projects in the developing world, he feels the first project has to target the high-end commercial market. “If it’s going to work, we have to find a private developer to do it,” he says. Twice he’s come close to building mass-timber high-rises for Canadian universities, but both projects stalled. “Everybody wants to build the third one,” he says. “But nobody’s stepped up to build the first one.”

Ian Gillespie, a Vancouver-based developer who worked with Green on one of those projects, at the Great Northern Way Campus in Vancouver, remains confident. “There’s a lot of money being spent trying to figure out all the code issues and seismic issues,” he says. “It isn’t just academic anymore. The forestry industry is interested in being part of the solution. There’s a better than realistic chance of this happening in the near future.”

In February, Green gave a presentation at the annual TED Conference, in Long Beach, Calif., where he shared a rendering of five wooden towers, up to 30 stories tall, on Roosevelt Island in New York. That image is part of MGA’s unsolicited proposal for a series of dorms, classrooms, and offices for the new Cornell NYC Tech campus, which will break ground in 2014.

Such publicity hasn’t always endeared Green to Vancouverites. “There are some people in this community who think Michael Green spends too much time being Michael Green,” Gillespie says. “He doesn’t fit in the typical Canadian architecture mold. But if you can’t sell yourself, and your dream, and your ideas, they don’t get off the ground.”

Whether Cornell seriously considers his proposal or not, Green remains confident that wood will be embraced. “You never see anyone walk into a building and hug a concrete column,” he says. “But a big wood column, it’s like an individual. You totally see people walk up and touch it. No two are the same. It’s much closer to people. It’s much closer to who we are.”